Convergence Issues 2D Airfoil

AeroEngiNerd · February 27, 2012, 11:31

I'm trying to run a low speed (M~0.3) 2D airfoil case in STAR-CCM+. I'm running into issues with convergence, specifically in y-momentum (it only drops about 1 order of magnitude, while the others drop 2-6). I was posting on here to hope someone could spot a rookie mistake that I'm making.

Domain - Rectangular domain, ahead of the airfoil 15 chords, behind 40, above and below 20.

I'm using an Inlet with specified speed, pressure outlet, and above and below are free-stream. The flow specifications were calculated based on a chosen temperature and velocity, and using atmospheric pressure.

The mesh is about 1 million cells, and the smallest cell size is approximately 0.005 in. I'm using a trimmed mesh and a prism mesh with 7 layers.

The solution is being run with a Coupled solver, with k-omega turbulence, and ideal gas flow.

Finally, while the solution is not "converged", it does seem to have the correct Cp shape. I haven't done detailed comparison of the Cp distribution, due to the lack of convergence. However, the Cp distribution does seem to be scalloped, or small peaks in the data on both the upper and lower surface about every 3-5% of the chord. Is this related to the lack of convergence or is this another issue entirely?

Any help you can provide would be most appreciated. Thank you in advance.

willimanili · February 28, 2012, 10:34

If your simulation isnt canceled due to divergence, dont look only at the normalized residuals to judge if your simulation is converged or not.
Create some reports of significant values like drag or lift force, velocities, pressure and so on and monitor them to judge the convergence.
Maybe the "Judging Convergence" chapter in the user guide help your understanding.

February 27, 2012, 11:31	Convergence Issues 2D Airfoil	#1
AeroEngiNerd New Member Aaron Kuenn Join Date: Feb 2012 Posts: 1 Rep Power: 0	I'm trying to run a low speed (M~0.3) 2D airfoil case in STAR-CCM+. I'm running into issues with convergence, specifically in y-momentum (it only drops about 1 order of magnitude, while the others drop 2-6). I was posting on here to hope someone could spot a rookie mistake that I'm making. Domain - Rectangular domain, ahead of the airfoil 15 chords, behind 40, above and below 20. I'm using an Inlet with specified speed, pressure outlet, and above and below are free-stream. The flow specifications were calculated based on a chosen temperature and velocity, and using atmospheric pressure. The mesh is about 1 million cells, and the smallest cell size is approximately 0.005 in. I'm using a trimmed mesh and a prism mesh with 7 layers. The solution is being run with a Coupled solver, with k-omega turbulence, and ideal gas flow. Finally, while the solution is not "converged", it does seem to have the correct Cp shape. I haven't done detailed comparison of the Cp distribution, due to the lack of convergence. However, the Cp distribution does seem to be scalloped, or small peaks in the data on both the upper and lower surface about every 3-5% of the chord. Is this related to the lack of convergence or is this another issue entirely? Any help you can provide would be most appreciated. Thank you in advance.

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February 28, 2012, 10:34		#2
willimanili Member Join Date: Feb 2011 Location: DE-PB Posts: 56 Rep Power: 15	If your simulation isnt canceled due to divergence, dont look only at the normalized residuals to judge if your simulation is converged or not. Create some reports of significant values like drag or lift force, velocities, pressure and so on and monitor them to judge the convergence. Maybe the "Judging Convergence" chapter in the user guide help your understanding.